Conventional open pit mining progressively follows an ore body using drilling and blasting, followed by shovel loading and truck haulage out of a pit. It is known to mine iron ore in large blocks using a series of benches so that various mining activities can be carried out concurrently (other than at actual blast times).
A bench of ore, for example 40 m long×20 m deep×10 m high and containing 8,000 tonnes of ore, is first drilled to form a pattern of “blast” holes and the residue therefrom, known as “blast cones”, is sampled and analysed, for example by chemical analysis, to determine whether on average the ore is (a) high grade, (b) low grade or (c) waste material. The cut-off between high and low grades is dependent on a range of factors and may vary from mine to mine and in various sections of a mine.
The bench of ore is blasted using explosives. The prime explosives used are ANFO (Ammonium nitrate/fuel oil) based and dispensed in specially designed bulk dispensing trucks which can regulate the explosive density prior to loading down the hole. The blasted material is picked up by electric rope shovels, diesel hydraulic excavators, or front-end haul loaders and placed into haul trucks and transported from the mine pit. The ore is processed outside the mine pit depending on the grade determination/assessment. For example, waste ore is used as mine fill, low grade ore is stockpiled or used to blend with high grade ore, and high grade ore is processed further as required to form a marketable product.
In conventional pit mining as described above, the ore grade assessments are made on the basis of material at spot locations only and the outcome of analysis of material can take many days which can delay the planning of blasting recovery and transport of the ore material.
Any reference herein to prior art is not to be taken as an admission as to the common general knowledge of a person skilled in the art.